1. Field of the Invention
The present invention relates to a fundus camera for diagnostic photographing of a fundus.
2. Description of the Related Art
A fundus camera photographs a peripheral part of a fundus as well as a central part of the fundus. When photographing a central part of the fundus, a fixation mark is projected along the optical axis of a photographing optical system on an eye to be inspected to align the visual line of the eye with the optical axis of the photographing optical system, and then the fundus of the eye is photographed. When photographing a peripheral part of the fundus, a fixation mark is projected in a direction different from the optical axis of the photographing system on the eye to direct the visual line of the eye in a direction different from the optical axis of the photographing system, and then the peripheral part of the fundus is photographed.
When photographing a peripheral part of the fundus by a conventional fundus camera, illuminating light projected by an illuminating optical system is reflected on the cornea and enters a photographing optical system, deteriorating the quality of a photograph. This problem will be explained with reference to FIGS. 12(a) and 12(b).
An illuminating optical system of a conventional fundus camera is provided with a cornea diaphragm (shading member) 1, an iris diaphragm 2, a lens diaphragm 3 and an objective 5. The cornea diaphragm 1, the iris diaphragm 2 and the lens diaphragm 3 prevents light rays from being reflected on the cornea, the iris and the back surface of the lens of an eye E to be inspected from entering a photographing optical system.
As shown in FIG. 12(a), when photographing a central part of the fundus Ef of the eye E, light rays passing an edge of the cornea diaphragm 1 are reflected by an aperture mirror (not shown), travel through the objective 5, fall on the eye E and are reflected by the cornea C in a direction diverting from a direction toward the objective 5. When the direction of the visual line of the eye E is changed to photograph a peripheral part of the fundus Ef, the aforementioned illuminating light rays are reflected by the cornea C toward the objective 5 as shown in FIG. 12(b), travel through the aperture of the aperture mirror, and enters a photographing optical system deteriorating the picture quality of photographs.
An object of the present invention is to provide a fundus camera capable of preventing the entrance of light rays reflected on the cornea in a photographing optical system when photographing a peripheral part of the fundus of an eye to be inspected, thereby providing a photographed image of an improved picture quality.
With the foregoing object in view, according to a first aspect of the present invention, there is provided a fundus camera comprising a main unit equipped with an illuminating system for illuminating the fundus of an eye to be inspected and a photographing system for photographing the fundus; a working distance detecting means for detecting whether a distance between the eye and the main unit is equal to a proper working distance or not; and a working distance changing means for changing the proper working distance depending on whether photographed part is a central part of the fundus or a peripheral part.
Even when photographing a peripheral part of the fundus, light reflected on the cornea does not enter the photographing system and, consequently, an image of an improved picture quality can be obtained.
According to a second aspect of the present invention, there is provided a fundus camera comprising an illuminating system for illuminating the fundus of an eye to be inspected, a photographing system for photographing the fundus, and shading members for preventing the entrance of illuminating light reflected on the cornea of the eye into the photographing system, the shape or the size of the shading members being changed depending on whether photographed part is a central part of the fundus or a peripheral part.
The effect of the fundus camera in the second aspect of the present invention is the same as that of the fundus camera in the first aspect of the present invention.